Distant retrograde orbit

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A distant retrograde orbit (DRO), as most commonly conceived, is a spacecraft orbit around a moon that is highly stable because of its interactions with two Lagrange points (L1 and L2) of the planet-moon system.


In more general terms, an object of negligible mass can be in a DRO around the smaller body of any two-body system, such as planet–Sun or exoplanet–star.

Using the example of a spacecraft in a DRO around a moon, the craft would orbit in the direction opposite to the direction in which the moon orbits the planet. The orbit is "distant" in the sense that it passes above the Lagrange points, rather than being near the moon. If we consider more and more distant orbits, the synodic period (the period between two moments when the craft passes between the planet and the moon) gets longer and approaches that of the moon going around the planet, so that the sidereal period (the time it takes for the craft to come back to a given constellation as viewed from the moon) can become much longer than the orbital period of the moon. An example with Europa has a sidereal period about eight times the orbital period of Europa, [1]

DROs have been researched for several decades, but as of 2022, no spacecraft have used such an orbit for an actual flight. [1]


The stability of a DRO is defined in mathematical terms as having very high Lyapunov stability, where an equilibrium orbit is "locally stable if all solutions which start near the point remain near that point for all time." [1]

Space concepts proposed to use a DRO

NASA Asteroid Redirect Mission (ARM)

By 2014, a lunar DRO was the preferred alternative under consideration for the NASA-proposed Asteroid Redirect Mission (ARM). This orbit would have had a lunar orbital altitude of approximately 61,500 km (38,200 mi), a distance somewhat greater than the distance from the Moon to either of the Earth-Moon L1 or L2 Lagrangian points. [1] NASA subsequently cancelled work on ARM in 2017 and never funded the build of flight hardware nor issued any space launch contracts. [2]

Jupiter Icy Moons Orbiter

A distant retrograde orbit was one of the proposed orbits around Europa for the Jupiter Icy Moons Orbiter—principally for its projected stability and low-energy transfer characteristics—but that mission concept was cancelled in 2005. [1]

NASA Lunar Gateway

Two system requirements for the NASA Lunar Gateway mention[ when? ] the use of lunar DRO's. Requirement L2-GW-0029, Single Orbit Transfer, states "the Gateway shall be capable of performing a single round trip transfer to Distant Retrograde Orbit (DRO) and back within 11 months." Requirement L2-GW-0026, Propulsion System Capability, states "the Gateway shall provide a fuel capacity that would support performing a minimum of two round-trip uncrewed low-energy cislunar orbit transfers between a near-rectilinear halo orbit (NRHO) and a distant retrograde orbit (DRO) and orbit maintenance for a period of 15 years between refueling." [3]

See also

Related Research Articles

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Halo orbit Periodic, three-dimensional orbit

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65803 Didymos Near-Earth asteroid in 2022

65803 Didymos is a sub-kilometer asteroid and synchronous binary system that is classified as a potentially hazardous asteroid and near-Earth object of the Apollo group. The asteroid was discovered in 1996 by the Spacewatch survey at Kitt Peak, and its small 160-metre minor-planet moon, named Dimorphos, was discovered in 2003. Due to its binary nature, the asteroid was then named Didymos, the Greek word for 'twin'.

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Subsatellite A satellite that orbits a natural satellite

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Asteroid Redirect Mission 2013–2017 proposed NASA space mission

The Asteroid Redirect Mission (ARM), also known as the Asteroid Retrieval and Utilization (ARU) mission and the Asteroid Initiative, was a space mission proposed by NASA in 2013. The Asteroid Retrieval Robotic Mission (ARRM) spacecraft would rendezvous with a large near-Earth asteroid and use robotic arms with anchoring grippers to retrieve a 4-meter boulder from the asteroid.

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Flyby (spaceflight) Flight event at some distance from the object

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Dimorphos Asteroid satellite

Dimorphos is a small asteroid satellite that was discovered in 2003. It is the minor-planet moon of a synchronous binary system with 65803 Didymos as the primary asteroid. After being provisionally designated as S/2003 (65803) 1 with informal nicknames such as "Didymos B" and "Didymoon", the Working Group Small Body Nomenclature (WGSBN) of the International Astronomical Union gave the satellite its official name on 23 June 2020. At a diameter of 170 metres (560 ft), it is one of the smallest astronomical objects that has been given a permanent name.

Power and Propulsion Element Power and propulsion module for the Gateway space station

The Power and Propulsion Element (PPE) previously known as the Asteroid Redirect Vehicle propulsion system is a planned solar electric ion propulsion module being developed by Maxar Technologies for NASA. It is one of the major components of the Gateway. The PPE will allow access to the entire lunar surface and a wide range of lunar orbits and double as a space tug for visiting craft.


  1. 1 2 3 4 5 Johnson, Kirstyn (18 December 2014). "Understanding NASA's Asteroid Redirect Mission : Distant Retrograde Orbits". Archived from the original on 11 January 2015. Retrieved 3 May 2015.
  2. Foust, Jeff (14 June 2017). "NASA closing out Asteroid Redirect Mission". SpaceNews . Retrieved 3 November 2019.
  3. "DSG-RQMT-001 - Gateway Program System Requirements Document (SRD)" (PDF). NASA Technical Reports Server. National Aeronautics and Space Administration (NASA). 2019. p. 25. Retrieved 11 April 2020.